Maize lethal necrosis disease

Maize dwarf mosaic virusis bad enough on its own for maize, sweetcorn, and sorghum. However, teamed with Maize chlorotic mottle virus, it can cause a disease that devastates maize and sweetcorn.

About maize dwarf mosaic virus (MDMV)

MDMV alone can cause serious disease in maize, sweetcorn, and sorghum. But it is also one of the viruses that cause maize lethal necrosis disease. This disease is caused by infection with 2 viruses at the same time:

Maize chlorotic mottle virus, and

MDMV (or one of its relatives).

Maize chlorotic mottle virus is not present in New Zealand.

Maize lethal necrosis disease

This disease has devastated maize crops in the United States (US), Mexico, and East Africa. In Kenya, it caused crop losses of between 50% and 100%.

Maize lethal necrosis disease kills the leaves of plants. Most infected plants die early or become sterile – so they can't produce pollen and seed.

Some maize varieties are resistant to the individual viruses. However, there don't seem to be maize varieties that can resist maize lethal necrosis disease.

Global distribution of MDMV

Why this is a problem for New Zealand

Plants infected with MDMV produce less grain and are often sterile. If plants are infected early in the season, the whole crop can be lost. Even without maize lethal necrosis disease, MDMV on its own could cause crop losses in New Zealand.

MDMV is often found in countries with similar climates to New Zealand. MDMV could establish in New Zealand anywhere that maize, sorghum, or other hosts are grown.

How it could get here

The virus could arrive in infected maize seeds. While the rates of seed infection are low, New Zealand imports a lot of maize seed.

New Zealand already has many aphid species known to carry and spread the virus. If infected plants were grown in New Zealand, aphids could rapidly spread the virus.

In other countries, MDMV also infects wild grasses that grow around the corn and sorghum fields. Aphids can then spread MDMV from the wild grass back into crops.

Biosecurity New Zealand has strict measures in place to limit the chances of MDMV, or its partner Maize chlorotic mottle virus, making it through the border.

How to identify MDMV

Symptoms can include:

yellower than normal leaves

reddish spots, streaks, and stripes on leaves

slow growth, so plants are often dwarfed

plants dying early

male and female flowers developing late or not developing normally – plants are often sterile

ears damaged with fewer kernels than normal.

Two sweet corn plants in the foreground infected by MDMV. Image: Public domain by Scot Nelson